Thyroid Disease Flashcards
Describe the hypothalamic-thyroid axis
- TRH is released from the hypothalamus and acts on the anterior pituitary
- Anterior pituitary releases TSH which binds to the TSH receptor on the follicular cells of the thyroid gland
- Thyroid gland releases hormones T3 and T4
T3 is the active form and T4 is converted into the active T3 close to target tissue
What proteins can T3 and T4 be bound to whilst in circulation?
- Transthyretin
- Thyroxine binding globulin
- Albumin
What receptor do thyroid hormones use to enter target cells
MCT8
What are the risk factors of thyrotoxicosis/hyperthyroidism?
- Family history of autoimmune thyroid disease
- Female
- Smoking
What are the most common causes of hyperthyroidism?
=> Graves Disease
Autoantibodies bind to TSH receptor in absence of TSH. Associated with autoimmune conditions and patients may go on to become hypothyroid or euthyroid
- Diffuse goitre
=> Toxic multinodular goitre
Nodules secreting thyroid hormones. Seen in elderly. Surgery indicated if compressive symptoms show (dysphagia, dyspnoea)
- Nodular goitre
- Patchy uptake of iodine
=> Toxic adenoma
Single nodule producing T3/T4 alone, due to self activating mutated TSH receptor. Isotope scan shows nodule is ‘hot’
=> Exogenous
Iodine excess
=> Ectopic thyroid disease
=> Drugs
AMIODARONE
=> Rarer cause:
- Subacute de Quervain Thyroiditis, associated with painful goitre, high temp and high ESR. Low isotope uptake on scan
What are the signs of Graves Disease?
- Exopthalmos
- Pretibial myxoedma
- Thyroid acropachy (clubbing)
What are the signs and symotoms of hyperthyroidism?
- Irritability
- Anxiety
- Weight loss
- Restlessness
- Heat intolerance
- Palpitations
- Increased sweating
- Tremor
- Diarrhoea
- Oligomenorrhoea (infrequent periods)
What is the normal process of thyroid hormone release?
- TSH from blood vessel binds to the TSH receptor on the follicular side of the follicular cell
- This promotes the up-regulation of thyroglobulin, which moves into the colloid
- Iodide ions also move into the cell from the circulation via I- channel, entering the colloid and combining with thyroglobulin
- The combination forms T3 and T4, which leave the cell
What are the investigations in thyroid related diseases?
=> Free T3/T4 (more useful than total and total is affected by thyroxine binding globulin levels) and TSH levels:
=> Hyperthyroidism suspected
- Measure T3, T4 and TSH levels
- T3 and T4 will be raised, TSH will be low
=> Hypothyroidism suspected
- Ask for only T4 and TSH, T3 adds no info
=> Elevated TSH receptor antibodies
Graves’ Disease (hyperthyroidism) (Some cases also see raised anti-TPO)
=> Elevated anti-TPO antibodies
Hashimoto’s Disease (hypothyroidism) (Some cases also see raised anti-TSH)
What is the management of hyperthyroidism?
=> Medical:
- Propranalol for rapid control of symptoms
- Carbimazole to reduce thyroid hormone levels through inhibition of thyroid peroxidase
- In cases of early pregnancy or first trimester, Propylthiouracil is used
- Levothyroxine may be given simultaneously with Carbimazole or Propylthiouracil to reduce chances of developing hypothyroid (block and replace therapy)
=> Surgery:
Thyroidectomy
=> Radiodine treatment:
- Contraindicated in pregnancy
- Contraindicated in thyroid eye disease
What is a thyroid storm?
- When large amount of thyroid hormones can cause coma, death and delirium
=> Management:
- IV fluids, NG tube insertion ad cooling
- Large dose of Carbimazole & Propanol + Potassium Iodide
- IV Hydrocortisone to inhibit conversion of T4 to T3
- B blockers for symptom control
In severe cases, patient is sedated. Thyroidectomy can be performed
What are the risk factors of hypothyroidism?
- Iodine deficiency
- Age
- Female
- Family History of autoimmune thyroiditis
What are the causes of hypothyroidism?
=> Autoimmune thyroiditis
(Hashimotos) MOST COMMON in developed countries
=> Subacute thyroiditis
Associated with painful goitre and high ESR and high temperature. Typically follows a viral infection
=> Post-partum thyroiditis
=> Riedel thyroiditis
Associated with painless goitre
=> Drug induced
- CARBIMAZOLE for hyperthyroidism
- LITHIUM
- AMIODARONE (can also cause hyperthyroidism)
=> Post thyroidectomy
=> Lack of Iodine
- MOST COMMON in developing world
What are the clinical features of hypothyroidism?
- Weight gain
- Tiredness
- Cold intolerance
- Anhydrosis
- Dry, thin hair
- Low mood
- Cold, yellow skin
- Carpal Tunnel Syndrome
- Constipation
- Menorrhagia
- Slow reflexes
What is the management of hypothyroidism?
- In a healthy, young patient, use LEVOTHYROXINE
- Lower does in elderly
- AMIODARONE (iodine rich drug)
- IV hydrocortisone should be given until adrenal crisis excluded
- Antibiotics
=> Check TSH
Interpreting TFTs
=> High TSH, low T4:
- Primary Hypothyroidism
=> High TSH, normal T4:
- Subclinical Hypothyroidism
=> High TSH, High T4, Low T3:
- Slow conversion of T4 to T3
=> Low TSH, T4 and T3 high:
- Primary Hyperthyroidism
=> Low TSH, normal T4 and T3:
- Subclinical Hyperthyroidism
=> Low TSH, low T4
- Secondary Hypothyroidism
=> Low TSH, low T4 and low T3:
- Sick Euthyroid
SUBCLINICAL MEANS THE TSH IS DERANGED BUT THE THYROID HORMONE LEVELS ARE NORMAL
What are the side effects of Carbimazole?
- Agranulocytosis
- Warn to stop and get FBC if any sign of infection
What is the biggest risk factor of Graves Disease?
Smoking
What is the management of Subclinical Thyroid Diseases?
=> Subclinical Hypothyroidism:
- Confirm elevated TSH is persistent, may have to recheck in a few months
- Treated if TSH elevated, +ve for thyroid autoantibodies, past Graves Disease, other organ specific autoimmunity
If TSH 4-10 mmol/L:
- If age < 65 with symptoms suggestive of hypo, treat with levothyroxine but stop if no imporvement
- If older, watch and wait
- If asymptomatic, observe and repeat test in 6 months
If TSH > 10:
- Start treatment if age > 70
- If older, watch and wait
=> Subclinical hyperthyroidism:
- Usually resolves itself
